I made an alfredo sauce last night using a roux made with ghee instead of regular butter, since that's what I had on hand. The ingredients were: ghee, flour, heavy cream, garlic, pecorino romano, and salt and pepper to taste.

The sauce turned out great, I was able to get the consistency to exactly how I wanted it.

When I went to reheat it in the microwave at work today for lunch, the sauce separated terribly, essentially leaving a pool of butter in the bottom of the bowl. It tasted ok, but it definitely felt like I was eating spoonfuls of butter at times. If it matters, the sauce and pasta were combined before microwaving, I didn't reheat the sauce by itself.

Is there a trick to reheating a homemade alfredo/béchamel sauce that will keep it from separating in the microwave? As suggested in this thread, could I add an emulsifier that will help the next day, but won't negatively affect the taste or consistency of the dish when it's still fresh?

Note: I posted this as a separate question from the one I reference above because this is specifically about separation during reheating, not storage, which might have different answers (such as lower temp or less time).

The way I avoid this issue at work is by eating my leftovers cold. Ok, yeah, the reason for that is that the office lacks a microwave oven, but hush. :-)
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MartiNov 3 '10 at 0:03

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Coincidentally, I just reheated a pesto cream sauce myself yesterday and didn't experience this problem at all. The sauce was basically made as a Béchamel with thawed pesto (made with olive oil) added to the roux and about half cream instead of milk. I didn't use any emulsifiers. I suspect that the generous amount of butter in the roux worked as a de facto emulsifier. So another option for you, next time, is to just use regular butter and not ghee. It's not a particularly efficient emulsifier like lecithin or xanthan, but it seems to do the trick in a cream sauce.
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Aaronut♦Nov 3 '10 at 15:12

Aaronut - great idea, I think this weekend I'll try it with the butter instead, otherwise keeping the recipe the same, and see how much of a difference I get. Though I'm definitely going to be buying some xanthan gum in the very near future.
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stephennmcdonaldNov 3 '10 at 16:01

3 Answers
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Sunflower lecithin (sorry, best link I could find) is gaining in popularity as an alternative to soy lecithin because it is widely perceived to have a neutral taste and actually has superior emulsifying properties. It's a little on the expensive side, though.

Soy lecithin by itself doesn't taste horrible if you buy it as a food additive (as opposed to a nutritional supplement). It's common to find in a lot of popular frozen pasta-and-sauce dishes, such as Michelina's, which obviously must be microwaveable without the sauce curdling or separating.

Another option is Sodium Stearoyl Lactylate, if you can get hold of it. This one adds a little sweetness which is generally pleasant-tasting, or at least inoffensive. You'll find it used most often as a dough conditioner or in baked goods, but another popular use for it is in commercial sauces, although unfortunately I can't find specific examples right now.

Mix in a little lecithin or xanthan gum as an emulsifier while the sauce is fresh or cooking and it's very unlikely that your sauce will separate, either in the fridge or in the microwave.

As for what you can do to specifically prevent separation while reheating, if you didn't add any emulsifiers in the first place... I really don't think there's anything you can do. If you're a slow enough eater the sauce will eventually separate right in front of you; that's just what happens when you have water and fat in the same sauce. Best to reheat on the stove top in that case, and stir frequently to prevent any further separation.

Hi @Aaronut. How much Xanthan gum is recommended? I noticed that the xanthan gum on the ingredients list in a Stouffer's fettuccine alredo was listed under the "less than 2%" part.
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Matthew MoisenDec 30 '14 at 21:22

@MatthewMoisen: It's going to depend on the recipe and how thick you want it - could be as little as 0.2% by weight, or as high as 1% (or even more if you want a super-thick sauce).
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Aaronut♦Dec 31 '14 at 3:01

Hey @Aaronut. Last week I did 0.1%, but it didn't form an emulsion as 5 minutes in the microwave the following morning resulted in the butter falling out of the solution. I'll try 0.2% tonight and report back. I was wondering, would microwaving for a long time possibly override the emulsion?
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Matthew MoisenJan 19 at 5:31

@MatthewMoisen: Enough heat can break any emulsion. The other answers here also apply - the longer you microwave and the higher the power, the more likely it is to break the emulsion. If it didn't separate in the fridge, I'd say the xanthan gum did work, at least somewhat. Try with lower heat next time.
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Aaronut♦Jan 19 at 6:17

Don't microwave at full power; I tend to go with 30-50% power for anything milk based, depending if you know you have a microwave that tends to be slower/faster than the recommended cook times on things.

And of course, check on it, possibly stir once it once or twice during re-heating so you don't develop hot spots. Yes, it'll take longer, but some things take time to keep from ruining.

And, like mfg mentioned, don't try to get it too hot ... or you could end up with the same results again.

I still have a little left (though I didn't bring it with me to work today); tonight I will have it as leftovers and try the lower temp/lower time idea and report back. Thanks for the advice!
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stephennmcdonaldNov 3 '10 at 16:02

The longer it is in the microwave the more the oil will separate. I guess the only recommendation is to nuke it to the minimum tolerable temperature. Try covering with a ceramic bowl or other insulator (phsycist?); I think it may do well to trap steam and add a second heating mechanic.